1. Field of the Invention
This invention relates to production of carbon anodes for use in producing aluminum, and more particularly, to a method and apparatus for automatically controlling the baking temperature of the raw anodes within close tolerances to produce uniformly baked anodes.
2. Description of the Prior Art
The present invention, by producing uniformly baked electrodes, is directed to decreasing the air pollution resulting from said manufacturing process; decreasing the fuel consumption utilized in such manufacturing process; and improving the quality of the anode thus produced. The attainment of each of these goals, through the use of the present invention, results in substantial benefits to the user of the present invention and to persons living near where the invention is practiced.
Exhaust gases from smokestacks of industrial furnaces are often a major source of air pollution. Because of present national concern about air pollution, the U.S. Congress created the Environmental Protection Agency (hereinafter EPA). This agency has promulgated various regulations governing the permissible industrial emissions into the atmosphere. Most states have established similar agencies which have promulgated identical or more stringent regulations. For example, the Commonwealth of Kentucky has enacted Title 401, K.A.R. chap. 3:060 (3) (a) 1, which states that the emission of particulate matter into the open air must not exceed 40% opacity, that is, the emission must not block more than 40% of the light passing through it. Not all attempts to limit the emissions of particulate matter from anode baking furnaces into the atmosphere have been successful. This is due to the nature of the heating processes and combustion apparatus utilized in the industrial processes. However, other attempts have been more successful. See for instance, U.S. patent application Ser. Nos. 119,918, 119,919, now U.S. Pat. No. 4,279,052, and 119,920, now U.S. Pat. No. 4,269,592, all filed on February 8, l980, and commonly assigned to the assignee herein. While the cited patent applications utilize improvements in an exhaust gas stream to achieve significant air pollution reduction, the present system, by automatically maintaining a predetermined desired anode baking temperature range, minimizes the hydrocarbons exiting from the plant smokestack.
In addition to national concerns about air pollution, it is also a national policy of the United States to conserve the amount of fossil fuel used in all sectors of the economy. Conservation, it has been argued, can extend existing energy supplies without the need for urgent exploration of additional fossil fuels. Accordingly, if a carbon anode bake ring furnace can be made to operate more efficiently with a lesser quantity of fossil fuel to produce the necessary heat, substantial reductions in fuel bills and pollution can be achieved. It has been calculated that approximately 44.1% of all energy inputted into a conventional carbon anode ring furnace is wasted. In fact, it has been determined that anodes produced by such a furnace consume only 21.6% of the total energy input into the furnace. By use of the present invention, the amount of wasted energy can be minimized. Thus, a very large reduction in fuel consumption can be attained, with the concomittant fuel cost savings.
The present invention is also directed to producing uniformly baked anodes of high quality and reproducibility. One of the factors which controls the ability to reproduce anode qualities is the temperature range within which the anode is baked. If the range of temperatures about a target temperature can be maintained within very small tolerances, for example, 1100.degree. C. plus or minus 5.degree. C., a substantially improved anode can be produced. For example, anodes that can be produced with a variation of 5.degree. about this point, rather than 50.degree. about this point, show an improvement in the range of finishing temperature by a factor of 10. As is well-known in the art, when utilizing such anodes, it is desirable that each anode have the same electrical resistance. This will cause the anodes to draw almost the same current and thus, in an electrolytic process for producing aluminum, produce a high purity product. The price obtained for this finished aluminum depends upon the percent purity of the finished product. The higher the purity, the greater the price obtained. Thus, it is to an aluminum producer's benefit to utilize anodes with as closely as possible the same resistance, in order to produce the highest purity end product, which in turn will bring the highest price.
As outlined above, the use of the present invention allows a carbon anode manufacturer to attain: reduced pollution; reduced fuel consumption and attendant fuel cost savings; and improved anode quality with attendant fuel cost savings; and improved anode quality with attendant higher purity aluminum produced and thus higher price obtained for the produced aluminum.
In the past, the uniformity of baked anodes depended directly upon the skill of firemen in controlling the baking process. Even with experienced firemen, a 50.degree. range of finishing temperature is generally the best that can be expected.
In addition to using firemen to bake the anodes, another system is known in the art. This system does not utilize a burner; rather, it uses a very crude lance to produce the heat for the furnace. Secondly, this system utilizes thermocouples to measure flue temperatures of the furnace. The use of thermocouples is troublesome because of the high temperatures inside the furnace. The thermocouples are hung vertically, and do not have a long life in such an environment. Also, the thermocouples must be moved every time the firing frames are moved, which is every day or two. This also tends to shorten thermocouple life. For these reasons, the use of thermocouples in such a system to indicate furnace temperatures is impractical since a great number of replacements are required. Replacements are both expensive and require additional personnel time to effectuate. For these reasons, these systems are not often utilized. One known installation of such a system is at the Intalco Aluminum Company, in Bellingham, Wash.
Other exemplary prior art industrial furnaces for baking aluminum products are shown and described in U.S. Pat. Nos. 2,678,205 and 4,128,394. However, these furnaces are of the tunnel kiln type and not of the ring pit type. Also, these patents do not disclose that any attempt has been made to obtain the greatest possible fuel efficiencies, the least possible pollution of the outside atmosphere and a great uniformity in the finished carbon baked products, utilizing computer control of the baking furnace.